title: Chromosomal variation in the tropical armoured catfish Callichthys callichthys (Siluriformes, Callichthyidae): implications for conservation and taxonomy in a species complex from a Brazilian hotspot.
abstract: The Neotropical catfish family Callichthyidae is characterized by wide karyotype variation, although reports are restricted to a few species/populations. This work provides new chromosomal information in two populations of armoured catfish (Callichthys callichthys) within the Atlantic forest boundaries in northeastern Brazil. Both populations of C. callichthys presented 2n=54 (16 metacentric, 24 submetacentric, 6 subtelocentric, and 8 acrocentric chromosomes) with occurrence of a metacentric B macrochromosome, reported for the first time in "2n=54" karyomorph. The lack of heterochromatin in the supernumerary chromosome suggests a recent origin of Bs with a significant difference in their frequency (p<0.05) between localities. Contrasting to the predominance of single nucleolus organizer regions (NORs) in other populations from South America, a remarkable polymorphism of 18S rDNA and GC-rich sites was detected, inasmuch as NOR phenotypes were unique for each individual, comprising up to 13 NOR-bearing chromosomes. The 5S rDNA was also mapped onto multiple chromosomes nonsyntenic to NORs. Such divergence in a number of NORs and occurrence of an euchromatic B chromosome in relation to other karyomorphs reinforces the divergent evolution of C. callichthys populations. Furthermore, these results also support central and drier Atlantic forest areas in northeastern Brazil as a biodiversity hotspot.
authors.affiliation: 1 Department of General Biology, State University of Londrina , Londrina, Brazil .
authors.forename: Josivanda Santos
authors.initials: JS
authors.lastname: Almeida
authors.forename: Paulo Roberto Antunes de Mello
authors.initials: PR
authors.lastname: Affonso
authors.forename: Débora
authors.initials: D
authors.lastname: Diniz
authors.forename: Paulo Luiz Souza
authors.initials: PL
authors.lastname: Carneiro
authors.forename: Ana Lúcia
authors.initials: AL
authors.lastname: Dias
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001938:Brazil; D002397:Catfishes / Q000235:genetics*; D002875:Chromosomes; D003247:Conservation of Natural Resources; D005260:Female; D014644:Genetic Variation; D008297:Male; D045483:Rivers